Looks pretty badass though I have to ask is it worth getting an unassembled kit when assembled alternatives exist? I haven't looked myself but I've heard these 'battery --> USB' type chargers were already being made (or are they).
One thing I'd be careful of is how reliable a charger is. Digital goods are extremely sensitive to voltage fluctuations so a poor weld or misweld/short etc... which doesn't clip the voltage to a very exact narrow range could end up bricking your phones. I ran into this concern when looking into the feasibility of just buying surplus broken solar cells and hooking them all up together to make a charger.
If I were to go the 'weld your own' route I'd want to make myself some insane electricity super-multi-tool which can convert any form of earth energy into any form of power. For example I'd have a solar charger, AA/AAA battery slots (and manual wire adapters for any other size), hydroelectric/wind power pinwheel, and manual induction magnet coil crank/shake/etc (i.e. even as far as pedometer type strapon device which uses leg motion to move the magnet in coil) for power charger all rolled into one. The outputs would be anything from raw power (cross the wires for fire! firestarter tool) to usb 5v, ac adapter ends (all sizes all voltages), step up circuitry and capacitors to make a stungun, etc etc... so that one can charge anything from any power source.
All of this would have to be lightweight/compact as possible and as rugged as possible to survive falls, scrapes, impacts, possible submergence in water if possible, extreme heat, et al... while not being too bulky. Then on top of all that made as cheaply as possible so that everyone can have one!